1. a main form with a button
2. clicking the main form button is opened a form with the grid and data
3. dblclick on a row (simulating something like a record selection that close the form) and the program raise the exception

Steps To Reproduce

Additional Information

To remove the problem I've to revert back the changes to previous version:

if FTitleArrowDown and (Button = mbLeft) then
begin
FTitleArrowDown := False;
if FTitleArrow and (dgTitles in Options) and (dgIndicator in Options) and
(Cell.X = 0) and (Cell.Y = 0) and (Columns.Count > 0) then
ShowSelectColumnClick; // Selection of columns
end;

I tried to reproduce the crash you saw by running your test application in Rio Update 1 and I cannot reproduce it. In my case double clicking on a row just closes the window.

So what's the difference between our systems:
- Windows 10 x64 in a VM Ware VM
- Delphi 10.3 Rio Update 1
- JCL and JVCL installed from a forked of the original Git repository,
but that fork kept in sync with the original JEDI repository